Monostable circuits for suppression of cathode ray beam when deflection voltages or currents fail



March 7, 1967 s. J. LENT 3,308,333

MONOSTABLE CIRCUITS FOR SUPPRESSION OF CATHODE RAY BEAM WHEN DEFLECTION VOLTAGES 0R CURRENTS FAIL Filed May a, 1964 2 She ets-Sheet 2 (3) LINE DRIVE CURRENT I l (d) LINE FL YBACK- L PULSE-S l A I |v l I I r l k I 2( TRIGGERS DERIVED! I r v K i (f) LINE [sue/(our Ll PuLs/ss v I 4BLACKLEVEL I 2 7 curoFr) LINE BLACKOUT MIXED BLACKOUT PULSES ATGR/D OF C.R.T

/ELL) BLACKOUT 4 FLg 2.

A/veA/rola A ITTOR/VE Y5 Unitedstates Patent Ofitice 3,308,333 Patented Mar. 7, 1967 3,308,333 MONOSTABLE CIRCUITS FOR SUPPRESSION F CATHODE RAY BEAM WHEN DEFLECTION VOLTAGES OR CURRENTS FAIL Stuart James Lent, Lower Kingswood, Surrey, England, assignor to The Marconi Company Limited, London, England, and Standard Telephones & Cables Limited, London, England, both British companies Filed May 8, 1964, Ser. No. 366,046 Claims priority, application Great Britain, May 14, 1963, 19,136/63 12 Claims. (Cl. 31520) The present invention relates to the protection of cathode ray tubes on failure of beam deflection voltages or currents. In tubes using high intensity electron beams, such as slide or film scanners for television for example, failure of deflection voltages or currents allow the beam to become stationary and damage part of the tube screen.

Previously, when line or field deflection voltages or currents have failed, such protection has been provided by an electromagnetic relay whose contacts cut .off the E.H.T. supply and electron beam focus current. Line and field deflection voltages or currents obtained from the deflection coils were rectified and used to control the relay. Failure of either of these voltages or currents to reach a predetermined amplitude caused the relay to operate, thus protecting the tube.

A disadvantage of such a protection circuit is that its speed of operation is, in some instances too slow; so that it only provides marginal protection.

The speed of operation is limited by the time constants of the rectifying circuits and the time lag of the relay.

According to the present invention there is provided a circuit arrangement comprising a cathode ray tube, a beam-deflecting circuit including a saw-tooth wave generator arranged to supply to the cathode ray tube a saw-tooth wave having a deflection portion and a fly-back portion, a monostable circuit having a period longer than that of the saw-tooth wave, coupled to an electrode of the cathode ray tube in such a manner that when the monostable circuit is in its stable state it applies to the electrode a beam-control voltage which suppresses the cathode ray beam or renders the beam innocuous to the screen of the tube, means for generating first and second triggering pulses occurring at or near the. beginning and end of each fly-back portion of the saw-tooth wave respectively and circuits for applying the second triggering pulses to trigger the monostable circuit from its stable to a quasi-stable condition and the first triggering pulses to trigger the monostable circuit from its quasi-stable condition to its stable condition.

During normal working the said control voltage may be used to provide black-out pulses to suppress the beam during fly-back.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which:

FIGURE 1 is a block diagram of a circuit according to the invention; and

FIGURE 2 shows waveforms at certain points in the circuit of FIGURE 1, these points having reference letters corresponding to those of the waveforms in FIGURE 2.

Referring to FIGURES 1 and 2, line synchronising drive pulses a are supplied at a terminal 10. A line time base circuit 12 produces from these line pulses saw-tooth line deflection currents c which are passed to line field deflection coils 13 of a cathode ray tube 14.

Field deflection currents are produced in a similar way from field synchronising drive pulses supplied to an input terminal 11 connected to a field time base generator 15 which feeds field deflection coils 16.

A monostable multivibrator 19 has two inputs each receiving trigger pulses from a shaping circuit 18.

During the fly-back interval of the saw-tooth wave a line fly-back pulse, d is produced from the line coils 13 and fed to the shaping circuit 18, which produces a from the trailing edge of this pulse a trigger pulse for The circuit arrangement may include any desired number of saw-tooth wave generators; for example in the case of a television tube a line time base and a field time base wave generator may be provided. Each of the wave generators is then associated with a separate monostable circuit and these circuits may be coupled in common to the said electrode.

The control voltage may be applied either to suppress the beam of electrons or to deform the beam or to deflect the beam olf the screen.

The first of the said pulses may be derived from the leading edge of drive pulses which drive the time base generator and initiate the fly-back of the saw-tooth wave and the second pulse may be derived fromthe trailing edge of a fiy-back pulse which is itself derived from the fiy-back portion of the saw-tooth wave.

The said control voltage of each of the monostable circuits may be developed across a common resistor which may be connected to the grid of the cathode ray tube.

The said monostable circuits may be monostable multivibrator circuits.

the multivibrator 19. This trigger pulse switches the multivibrator from its stable to a quasi-stable state. The duration of the quasi-stable state is arranged to be longer than the period of the saw-tooth wave.

Each line drive pulse is fed through a connection 17 to the shaping circuit 18, which derives thereform a secondtri'gger pulse b derived from the leading edge of the line drive pulse. This second trigger pulse when fed to the multivibrator 19 switches it from its quasi-stable state to its stable state. i

The field trigger circuit 20 and the field multivibrator 21 function in a siinilar way to the circuits 18 and 19, the multivibrator being switched to a quasi-stable state atthe end of the field fly-back interval and to its stable state at the beginning of the fly-back interval.

Both multivibrators are so biased that in their stable states current flows through their output anodes and a common load 22, thus producing a low potential at the point 24. The grid 23 of the tube is connected directly (or through an aperiodic network) to the point 24 and therefore the beam is cut off when either or both the multivibrators is in its stable state.

Considering the cycle of operation of the line multivibrator, this is first switched to its quasi-stable state at the end of the line fly-pulse d and ceases to suppress the beam. At the beginning of the next line fiy-back pulse the multivibrator is switched back to its stable state and the beam is again suppressed. The negative-going pulses 1 produced at the point 24 by the line multivibrator only are used to provide black-out pulses cutting off the beam during fiy-back. If the deflection current fails when the multivibrator is in its quasi-stable state it will return to its stable state at the end of the quasi-stable state period. The multivibrator will then remain in its stable state since the switching pulses e derived indirectly from the deflection current will not occur. For the same reason if the deflection current fails when the multivibrator is in its stable state, it will remain in that state.

tional circuit using a relay to cut ofi the E.H.T. and the beam focus current.

The output voltage across the resistor 22 can also be used to control thetube E.H.T. and beam focus current, by operating a relay for example, and thus providing follow up protection. c

The beam control voltages may, after amplification if necessary be used in other ways to suppress the beam, for example by deflecting the beam from the screen by cutting off the E.H.T. supply to the tube. Alternatively the suppression voltages may be used to defocus the beam.

I claim: r

1. A circuit arrangement including,

a cathode ray tube, a control means for said tube, means for deflecting the cathode ray beam of said tube,

a saw-tooth wave generator generating a saw-tooth wave having a deflection portion and a fly-back portion,

means coupling said saw-tooth wave generator to said beam deflecting means,

a monostable circuit having a period longer than that of said saw-tooth wave and producing a beam-control voltage when in its stable condition, means coupling said monostable circuit to said control means and thus applying said control voltage to said control means to render the cathode ray beam innocuous I to the screen of the said cathode ray tube,

a generating means for generating first and second triggering pulses occurring substantially at the beginning and end respectively of said fly-back portion of said saw-tooth wave, 1

means for applying said second triggering pulses to said monostable circuit to trigger it from its stable condition to a quasi-stable condition, and for applying said first triggering pulses to said monostable circuit to trigger it from its quasi-stable condition to its stable condition.

2. A circuit arrangement according to claim 1 wherein the said control means includes an electrode to suppress the said beam when the said control voltage is applied thereto.

3. A circuit arrangementaccording to claim 2 including means for coupling drive pulses to said generating means, and wherein said generating means includes means for initiating the fly-back portion .of said saw-tooth wave, and 1 means for deriving said first triggering pulse from th leading edge of said drive pulses.

4. A circuit arrangement according to claim 3 including means for coupling said saw-tooth wave generator to said generating means and thus applying at least the flyback portion of the said saw-tooth wave to said generating means, and wherein said generating means includes means for generating a fly-back pulse from the said flyback portion and means for deriving said .second pulse from the trailing edge of said fly-back pulse.

5. A circuit according to claim 4 wherein said means coupling said monostable circuit to said control means applies said control voltage to said control means as a black-out pulse during said fly-back portion of said sawtooth wave. a

6. A circuit arrangement according to claim 5 wherein said monostable circuit is a monostable multivibr ator c rcuit.

7. A circuit arrangement including,

a cathode ray tube, a control means for said tube,

first and second means for deflecting the cathode ray beam of said tube, first and second saw-tooth wave generators, generating first and second saw-tooth waves respectively, each having a deflection portion and a fiy-back portion, first and second means coupling said saw-tooth wav'e generators to said first and second deflection means respectively, first and second monostable circuits having periods longer than those of said first and second saw-tooth wave generators respectively, and

producing first and second control voltages respeetively when in their stable conditions,

first and second means couplingsaid first and second monostable circuits to said control means andthus applying said first and second control voltages to said control means to render the beam innocuous to the screen of said cathode ray tube,

first and second generating means for generating first 8. A circuit according to claim 7 wherein said first saw-tooth wave generator is a line time-base generator and said second saw-tooth wave generator is a field timebase generator.

9. A circuit according to claim 8 wherein said control means includes a resistor and said first and second means coupling said monostable circuits to said control means apply said first and second control voltages to said resistor.

10. A circuit according to claim 9 wherein said control means includes an electrode and means coupling the said resistor to the said electrode for applying the said first and second control voltages to said electrode on failure ofeither of the" said deflection portions of the said first and second saw-tooth waves, and as black-out pulses during the fly-back portions of the said saw-tooth waves.

11. A circuit according to claim 10 including first and second coupling means for coupling first and second drive pulses to said first and second generating means respectively, and wherein said first and second generating means include means for initiating the fly-back portion of said first and second saw-tooth waves respectively and means for deriving said first and second triggering pulses from the leading edges of said first and second drive pulses respectively.

12. A circuit arrangement according to claim 11including first and second means for coupling said first and second saw-tooth wave generators to said first and second generating means respectively and thus applying at least the fly-back portion of the said first and second sawtooth wave generators to said first and second generating means respectively, and wherein said first and second generating means include means for generating first and second fly-back pulses respectively from said first and second fly-back portions, and means for deriving said second and fourth pulses from the trailing edges of said first an second fiy-back pulses respectively.

- References Cited by the Examiner UNITED STATES PATENTS 2,860,283 11/1958 Horowitz 3152Q DAVID G. REDINBAUGH, Primary Examiner.

T. A. GALLAGHER, Assistant Examiner. 

1. A CIRCUIT ARRANGEMENT INCLUDING, A CATHODE RAY TUBE, A CONTROL MEANS FOR SAID TUBE, MEANS FOR DEFLECTING THE CATHODE RAY BEAM OF SAID TUBE, A SAW-TOOTH WAVE GENERATOR GENERATING A SAW-TOOTH WAVE HAVING A DEFLECTION PORTION AND A FLY-BACK PORTION, MEANS COUPLING SAID SAW-TOOTH WAVE GENERATOR TO SAID BEAM DEFLECTING MEANS, A MONOSTABLE CIRCUIT HAVING A PERIOD LONGER THAN THAT OF SAID SAW-TOOTH WAVE AND PRODUCING A BEAM-CONTROL VOLTAGE WHEN IN ITS STABLE CONDITION, MEANS COUPLING SAID MONOSTABLE CIRCUIT TO SAID CONTROL MEANS AND THUS APPLYING SAID CONTROL VOLTAGE TO SAID CONTROL MEANS TO RENDER THE CATHODE RAY BEAM INNOCUOUS TO THE SCREEN OF THE SAID CATHODE RAY TUBE, A GENERATING MEANS FOR GENERATING FIRST AND SECOND TRIGGERING PULSES OCCURRING SUBSTANTIALLY AT THE BEGINNING AND END RESPECTIVELY OF SAID FLY-BACK PORTION OF SAID SAW-TOOTH WAVE, MEANS FOR APPLYING SAID SECOND TRIGGERING PULSES TO SAID MONOSTABLE CIRCUIT TO TRIGGER IT FROM ITS STABLE CONDITION TO A QUASI-STABLE CONDITION, AND FOR APPLYING SAID FIRST TRIGGERING PULSES TO SAID MONOSTABLE CIRCUIT TO TRIGGER IT FROM ITS QUASI-STABLE CONDITION TO ITS STABLE CONDITION. 